In the prior art, on-board aircraft monitoring means bring a computer implementing several, typically three, redundant computing channels into play, as shown in FIG. 1. Two computing channels are called redundant when the channels are comprised of the same hardware and software elements. Thus, the channels are theoretically identical and, still theoretically, should provide identical results. The utilization of three redundant computing channels ensures adequate processing of the drift from one of the computing channels.
Thus, as illustrated in FIG. 1, a first computing channel 101, a second computing channel 102 and a third computing channel 103 are schematically represented. The channels are referred to as primary computing channels since they are the computing channels present in computers from the prior art. The channels are also routinely called critical computing channels, where the term “critical” refers to the position since position is used for critical applications. The three primary computing channels are redundant. All the channels simultaneously produce primary computing cycles that each result in obtaining a primary three-dimensional position of the aircraft, respectively referred to as 3D Position No. 1, 3D Position No. 2, and 3D Position No. 3. These three primary positions, obtained simultaneously, are then sent to a computer 104 whose role is to consolidate the results provided by the primary computing channels. Therefore, if one of the three primary positions is completely incoherent with relation to the two others, it is not taken into consideration in the development of a consolidated aircraft position 105 that will subsequently be used, particularly in critical applications.
However, such an organization does not allow the organization alone to manage the onset of common-mode failures. Such failures generally affect mainly most, if not all, redundant aircraft position computing channels. These breakdowns may, for example, have at their origin coding errors, a breakdown of a hardware component intervening in the redundant computing channels, external circumstances such as lightning, a GPS receiver common-mode failure or a problem known as multipath GPS, in which the GPS signal is reflected on the ground before returning to the aircraft sensors.
Therefore, a common-mode failure results, in most cases, in three incoherent results and comparable values being obtained, none of which may then be distinguished and no error may be detected. Consequently, during difficult piloting operations such as stand-alone approaches or low-altitude flights, during which the dissimilar conventional aircraft position monitoring means are no longer available, no common-mode failure detection means exist.